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 Originally Posted by Photo Engineer  Mix your cyanotype as usual and add to it some gelatin to thicken it as desired then add some surfactant and coat. Okay, time to report back.I tried with RC paper and it didn't work. The emulsion washes right off in the wash. Photo-flow does make it easier initially to coat it, but no help if it doesn't survive the wash.
I must admit I am still a bit muddy on the gelatin instruction. Doesn't gelatin need to be dissolved in warm water? I tried just tossing in some gelatin in the sensitizer but to no avail. Maybe I'll try sizing the paper with gelatin the conventional dip-and-dry way - or maybe this whole recycling silver RC paper isn't going to work.
Good news is, my cyanotypes on more conventional paper did come out looking great.
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Ok, to 100 grams of sensitizer, add 10 grams of gelatin and heat to 40C. Hold this until all gelatin has dissolved. Add to this, 5 cc of 10% Glyoxal or 10% Chrome alum and a few drops of surfactant. Coat. Let stand for at least 4 hours, preferrably 8 hours. This will harden.
The Glyoxal comes as 40% solution and dilution to 10% makes a 4% solution. Don't worry, I call it 10% because it is 10% of the commercial product.
PE
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An alternative, which I use is to take 50 grams of sensitizer and 50 grams of pre-prepared 20% gelatin and melt this at 40C. This is more dilute and requires a heavier coat of the sensizer gelatin. Use the same amount of hardener and surfactant.
PE
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Thanks a lot for that. Will give it a try.
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A while ago I tried using fixed, expired, FB paper for cyanotypes and would say that it was very successful. Coating the paper is a nightmare as the sensitiser solution 'beads up'. I overcame this by repeatedly brushing until the solution had dried enough. It also needed at leat two coats.
Soaking the paper before hand definitely helped and I'll have to give the photo-flo trick a go as I've recently got a new split back frame I want to try out with something.
Here's some examples. The traditional cyan image is 100% APUG friendly, you don't want to know where the source image of the coffee stained chilies came from but I'm showing it here as the resultant cyanotype is a good example of what can be acheived on old FB paper.
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@crispinuk - the chili image is wonderful, the coffee makes a nice warm background for the subject, and I like the edge effects where the negative didn't cover the entire paper.
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Originally Posted by Photo Engineer to 100 grams of sensitizer, add 10 grams of gelatin and heat to 40C. Hold this until all gelatin has dissolved. Add to this, 5 cc of 10% Glyoxal or 10% Chrome alum and a few drops of surfactant.
PE
PE,
I have been following this thread with interest and am thinking of having a go, I just have one hesitation:
the only hardener I have in stock is formalin, will this react to the sensitiser in any way. I normally use it for hardening pure gelatin size for gum printing.
are there any contradictions i should know about? I don't want to make anything nastier than formaldehyde fumes! I will be using traditional cyanotype and maybe agyrotype
cheers
pete
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Pete;
All formalin and glyoxal type hardeners will react with ferricyanide with time. Therefore, time and heat are your enemy once you mix the hardener into the sensitizer. Also, if you add too much, the paper can turn blue with time. This is the general problem you will have coating with a hardener. In fact, it is a problem with silver halide as well. Aldehyde hardeners gradually fog films and papers.
PE
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thanks for your swift reply!
I guess the way to go would be to add the hardener by the drop to the required amount just before coating, as i do with sizing. I will try a couple of experiments to see how it goes...now that i know i am not risking any unpleasant chemical reactions!:o
the depth of your knowledge continues to impress me 
cheers
pete
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Pete;
I make 120 ml batches and coat about 12 ml per square foot of the mix which is as described above, 50% senstizer and 50% gelatin so that the final solution is 10% gelatin. It takes me about 1 hour to prepare and then coat the 10 sheets or so that I usually make.
I coat on plain uncoated baryta. The glossy cyanotype you can get is quite beautiful.
PE
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